Gas turbine engines are typically employed to power aircraft. Typically a gas turbine engine will comprise an axial fan driven by an engine core. The engine core is generally made up of one or more turbines which drive respective compressors via coaxial shafts. The fan is usually driven directly off an additional lower pressure turbine in the engine core.
The air is generally compressed firstly in an intermediate pressure compressor and then in a high pressure compressor. Each stage of the compressor typically utilises multiple discs each with a set of rotor blades of aerofoil cross section. The discs are often bolted or welded together to form a compressor drum. The rotor blades and discs may be in the form of a blisk, or alternatively the blades may be connected to the disc via grooves provided in the disc.
The blades can be mounted either axially, where a series of slots are provided in the disc to receive a dovetail or fir tree blade root, or the blades can be mounted circumferentially.
Circumferential mounting will now be described in more detail with reference to FIG. 1. A disc 153 is provided having a groove 154 that extends circumferentially around the periphery of the disc. The roots 50 of the compressor blades 40 are received in the circumferential groove via a loading slot. Each compressor blade is adjacent a neighbouring compressor blade with a platform 47 of the blade acting to space the aerofoil portion of the blades apart. A locking device, e.g. a locknut 39 and jack screw, is then used to secure the blades 40 in the groove 154.
It is necessary to machine the groove 154 with high precision to restrict the stress experienced by the compressor blade and groove during operation of the compressor.